Kenwood TS-440S Serivce Manual page 11

TS-440 $
CIRCUIT DESCRIPTIO N
DSB by IC4 goes through the SSB transmit switching diode s
D17 and D18, filter switching diodes D14 and D12, and SS B
ceramic filter CF1, to obtain the SSB signal . The SSB signa l
then goes through the transmit switching diode D36 and i s
fed into the transmit first mixer, IC6, where the SSB signa l
is mixed with the output from the 8 .375 MHz oscillator i n
the IF unit, and converted to 8 .83 MHz . In CW or FM mode ,
the carrier signal from the PLL unit does not go through IC 5
BM or the 455 kHz filter . These carrier signals are applie d
to IC6 via switching diodes D53 and D54 . The output signa l
from IC6 goes through the MCF to remove spurious compo -
nents, and is amplified by the IF amplifier Q46 (3SK73) an d
sent to the RF unit . Q46 provides ALC control and C W
keying .
In the transmitter second mixer, consisting of Q1 1 and Q12 ,
(3SK122), the 8 .83 MHz transmit IF signal input to the R F
unit is mixed with HET oscillator signal (36 .22 MHz) fro m
the PLL unit and converted to 45 .05 MHz signals . The 45 .0 5
MHz signal goes through D23 and the MCF to remove an y
spurious components . The 45 .05 MHz signal then goe s
through D27 and is supplied to the transmit third mixer con -
sisting of Q13 and Q14 (3SK1 22) . In the third mixer the sig -
nal is mixed with VCO signal (Q21 to Q24) amplified by Q1 2
(2SC2668) and converted to the required transmit frequen -
cy (1 .8 to 29 .7 MHz) . The signal from the third mixer goes
through the low pass filters C156, C158, C159, and L89 ,
and is amplified by the wide band amplifier Q15 (2SC2570) .
The signal then goes through the wide band transformer Ti 9
and low pass filters C164, C165, and L90, and is further am -
plified by wide band amplifier Q16 (2SC2538) . The signa l
from the Q16 goes through the output transformer T20 an d
is used as the drive output .
In FM mode, the PLL VCO is directly modulated . The audi o
signal from IF unit IC4 (UPC1 1 58HZ) is fed into the RF uni t
via the FM1 pin . In the RF unit, the audio signal is amplifie d
by Q36 (2SC2459) and Q37 (2SC2603), and goes throug h
the limiter circuit consisting of Q38 (UPC4558C) and lo w
pass filter circuit, and is sent to the PLL unit via the FM D
pin . In the PLL unit, the 36 .22 MHz VCO is modulated . Q3 9
(2SC2603) is a switching circuit to prevent the modulate d
signals from being emitted from the PLL unit in a mode othe r
than FM .
For "S" model radios the output from the RF unit i s
amplified to a 100 W power level by Q1 (2SC2075), Q 2
and Q3 (2SC2509), and Q4 and Q5 (2SC2879) in th e
final unit . The 100 W output goes through the LPFs whic h
differ by bands, and is sent as output to the antenna via th e
AT unit and transmit/receive switching relay . SWR an d
ALC detection is performed at the output of the LPFs .
1) Antenna tune r
The antenna tuner operates when the AUTO/THRU switc h
is in the AUTO position and the AT TUNE switch is ON . Th e
antenna tuner is driven in the CW mode and power is reduce d
to 50 W by the microcomputer regardless of the mode select -
ed before the AT TUNE switch was turned ON . The rang e
of operating frequencies is determined by a microcompute r
program, and is from 3 .5 MHz to 30 MHz .
• AT unit operatio n
Power transmitted by the final unit passes through the cur -
rent and voltage detecting transformers L1 and L2 usin g
toroidal cores . Current and voltage components detecte d
by the transformers are supplied to pins 9 and 13 of IC 2
for wave shaping and their phases are compared by IC 3
HD10131 . The output from pin 3 of IC3 depends upo n
the phase of the voltage and current waveforms applie d
to IC3 . The signal from IC3 pin 3 is sent to pins 10 an d
15 of buffer IC IC3 HD10125 . Output from pins 12 an d
13 of IC3 goes through level shift Zener diodes D5 an d
D6 to control the input circuit of motor drive IC IC 5
BA6109U2 . The output signal is used to drive motor M 1
to adjust the variable capacitor VC1 so that the phas e
difference between voltage and current components i s
reduced .
The current and voltage components output from the cur -
rent and voltage detecting transformers is also supplie d
to the voltage comparator IC1 NJM2903D . The compa-
rator output is used by motor drive IC IC6 BA6109U2 t o
drive motor M2 to adjust variable capacitor VC2 so tha t
the amplitude difference is reduced . That is, the phase con -
trol variable capacitor VC1 is controlled so that the cur -
rent is in phase with the voltage and the voltage contro l
variable capacitor VC2 is controlled so that the amoun t
of amplitude difference between the current and voltag e
is reduced (SWR1, an SWR of 1 to 1, is obtained whe n
the current and voltage are in phase and the amount o f
amplitude difference is 0) . VC1 and VC2 are designed t o
operate independently of each other, but since phas e
difference affects the amount of amplitude difference an d
vice versa, VC 1 and VC2 will normally rotate together .
Forward and reflected waves detected by the filter unit ar e
converted to SWR control signals in the SWR arithmetic cir-
cuit in the control unit and are sent to the ISW pin of th e
AT unit . Since the SWR control signals are current wave -
forms, the signals are converted from Ito V waveforms b y
IC8 (b/4) in the AT unit and to obtain the corresponding vol -
tage mode SWR signals are generated . The SWR signals ar e
then fed into the SWR comparator IC8 (C/4) . The referenc e
voltage pin 9 of the IC8 (C/4) is supplied with a voltage cor -
responding to an SWR of 1 .25 to 1 via a potentiometer .
Therefore, when the actual SWR value exceeds 1 .25, pin 8
of SWR comparator IC8 (C/4) is H, so the motor drive vol-
tage control transistor Q5 turns on and the collector of Q 4
is supplied with voltage from pin 14S . The voltage is als o
used to turn the tuning LED on . The inverted input pin of IC 8
(d/4) is supplied with triangular waves generated by IC7, an d
its non-inverted input pin is supplied with the above SWR vol -
tage signals . As a result, as SWR lowers, IC8 (d/4) outputs
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